Tibial condylar hemiplasty implants, anchor assemblies, and related methods

ABSTRACT

A method for mounting a tibial condylar implant includes forming a tunnel having a proximal end on a lateral, medial, or anterior side of a proximal end of the tibia and a distal end on an at least partially resected lateral or medial facet at the proximal end of the tibia. A condylar implant is positioned over the distal end of the tunnel. A fastener is advanced into the tunnel from the proximal end of the tunnel. The fastener which is at least partially disposed within the tunnel is secured to the condylar implant.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to tibial condylar hemiplasty implants,anchor assemblies used to secure such implants to the tibia, and therelated methods.

2. The Relevant Technology

The knee joint comprises two generally rounded condyles, i.e., lateraland medial condyles, that are located at the lower or distal end of thefemur. These femoral condyles are disposed above corresponding lateraland medial condyles located at the upper or proximal end of the tibia. Aflexible meniscus provides cushioning between the opposing matchingpairs of condyles.

As a result of injury, wear, disease or other causes, it is occasionallynecessary to replace all or part of the knee joint. Knee replacementstypically entail cutting off or resecting both of the femoral condylesand the tibial condyles. Complementary artificial implants are thenmounted on the distal end of the femur and the proximal end of thetibia. Where only one condyle has been injured, more recent proceduresprovide for partial knee replacement. In this procedure, only one of thelateral or medial femoral condyles is resected. The corresponding one ofthe lateral or medial tibial condyles is also resected. Implantsreferred to as “unicondylar” implants are mounted on the resected areaof the femur and tibia.

Although knee replacements have met with success, one of the significantdrawbacks to knee replacements is the recovery. Traditional kneereplacements, both full and partial, require an open procedure whereinrelatively large incisions are made so as to fully expose the respectiveends of the femur and tibia. This exposure is necessary when usingconventional techniques to resect the femur and tibia and for mountingthe implants. For example, conventional tibial implants are screweddirectly into the resected end face of the tibia. Mounting such screwsrequires exposure of the resected end face. In yet other embodiments,projections are formed on the implants which are received within slotsformed on the resected end face of the tibia. Again, forming of theslots and inserting the implant into the slots requires substantiallyfull expose of the resected end face of the tibia.

In general, the more invasive the surgery, the more difficult and timeconsuming the patient recovery. Furthermore, such open and invasivesurgeries have a greater risk of infection.

Accordingly, what is needed are systems and methods for resecting andmounting a condylar implant on the tibia that uses procedures thatminimize incisions, the amount of bone resection, and/or the impact onsoft tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of the proximal end of a tibia;

FIG. 2 is a perspective view of a guide assembly for forming a tunnel onthe proximal end of the tibia shown in FIG. 1;

FIG. 2A is a perspective view of an alternative template used with theguide assembly shown in FIG. 2;

FIG. 3 is a perspective view showing the guide assembly in FIG. 2mounted on the tibia of FIG. 1;

FIG. 4 is a perspective view of the tibia shown in FIG. 1 having atunnel formed thereon;

FIG. 5 is a perspective view of a rasp assembly resecting the tibia ofFIG. 4;

FIG. 6 is a top perspective view of the raps assembly shown in FIG. 5;

FIG. 7 is a bottom perspective view of the rasp assembly shown in FIG.6;

FIG. 8 is an exploded perspective view of the retention rod shown inFIG. 5;

FIGS. 9A and 9B are perspective views of the retention rod shown in FIG.8 being mounted to the rasp assembly shown in FIG. 5;

FIG. 10 is a perspective view of the tibia shown in FIG. 4 having arecess formed thereon;

FIG. 11 is a perspective view of a cutting template being mounted on thetibia shown in FIG. 4;

FIG. 12A is a top perspective view of a condylar implant;

FIG. 12B is a bottom perspective view of the condylar implant shown inFIG. 12A;

FIG. 12C is an exploded perspective view of the condylar implant shownin FIG. 12B;

FIG. 13 is a perspective view of an alternative embodiment of a condylarimplant;

FIG. 14 is a perspective view of another alternative embodiment of acondylar implant;

FIG. 15A is a top exploded perspective view of the condylar implantshown in FIG. 14;

FIG. 15B is bottom exploded perspective view of the condylar implantshown in FIG. 15A;

FIG. 16A is a top exploded perspective view of an alternative condylarimplant;

FIG. 16B is bottom exploded perspective view of the condylar implantshown in FIG. 16A;

FIG. 17 is an exploded view of an anchor assembly for securing acondylar implant to the tibia shown in FIG. 10;

FIG. 18 is a side view of the fastener of the anchor assembly shown inFIG. 17 being secured to the condylar implant positioned on the tibia;

FIG. 19 is a cross sectional perspective view of the bone anchor of theanchor assembly shown in FIG. 17;

FIG. 20 is a side view of the bone anchor shown in FIG. 19 being FIG. 17to the tibia shown in FIG. 18;

FIG. 21 is a side view of a crown nut of the anchor assembly shown inFIG. 17 being mounted to the fastener shown in FIG. 18;

FIG. 22 is a cross sectional side view of the assembled anchor assemblyshown in FIG. 17 securing the condylar implant to the tibia;

FIG. 23 is a perspective view of an alternative embodiment of thefastener shown in FIG. 17;

FIG. 24 is an alternative embodiment of an anchor assembly;

FIG. 25 is a cross section side view of the anchor assembly shown inFIG. 24 securing a condylar implant to a tibia;

FIG. 26A is a top perspective view of an alternative embodiment of acondylar implant;

FIG. 26B is a bottom perspective view of the condylar implant shown inFIG. 26A;

FIG. 27A is a top perspective view of another alternative embodiment ofa condylar implant; and

FIG. 27B is a bottom perspective view of the condylar implant shown inFIG. 7A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to methods and apparatus for preparing andmounting a condylar implant on a tibia of a patient. The methods andapparatus are designed so that the condylar implant can be mounted usingprocedures that are minimally invasive. As a result, recovery time issignificantly improved while the risk of infection minimized.

Depicted in FIG. 1 is a proximal end 10 of a tibia 12. Proximal end 10has a lateral side 14 and a medial side 16 which each extend between ananterior side 18 and a posterior side 19. Proximal end 10 furthercomprises a lateral condyle 20 and a medial condyle 21. Lateral condyle20 terminates proximally at a lateral facet 22 of a superior articularsurface of tibia 12 while medial condyle 21 terminates proximally atmedial facet 24 of a superior articular surface of tibia 12.

Although tibia 12 shown in FIG. 1 is from a left leg, it is appreciatedthat the tibia of the right leg has a complimentary configuration andthat the methods and apparatus disclosed herein are equally applicablethereto. Furthermore, the methods and apparatus disclosed herein areprimarily illustrated in association with medial condyle 21 of tibia 12.It is also appreciated that the methods and apparatus can be used inassociation with lateral condyle 20.

In one embodiment, to facilitate mounting of a condylar implant onmedial condyle 21, conventional arthroscopic procedures are used toresect the posterior portion of the medial meniscus. Once the posteriorportion of the medial meniscus is removed, a vertical or horizontalincision, generally in a range between about 2 cm to about 6 cm, isformed over the anterior side of the medial meniscus. Followingretraction of the surrounding tissue, the anterior side of the medialmeniscus is resected. A coarse rasp is then inserted between the medialcondyle of the femur and medial condyle 21 of tibia 12. The rasp is usedto remove approximately 1-2 mm of articular cartilage on medial facet 24of tibia 12. Removal of the meniscus and the articular cartilageprovides increased access to medial facet 24 of tibia 12.

Depicted in FIG. 2 is one embodiment of a guide assembly 30 which is nowused for forming a tunnel through a portion of tibia 12. As discussedbelow in greater detail, the tunnel can be used for preparing tibia 12for a condylar implant and/or securing a condylar implant to tibia 12.In general, guide assembly 30 includes a substantially U-shaped guidebrace 32 having a template 34 and a tubular guide sleeve 36 mounted onopposing ends thereof. More specifically, guide brace 32 has a first end38 and an opposing second end 40. Recessed in first end 38 is a socket42.

Template 34 comprises a low profile base plate 44 having a top surface46 and an opposing bottom surface 48 which each extend between a firstend 50 and an opposing second end 52. Although not required, in oneembodiment bottom surface 48 has a configuration generally complementaryto medial facet 24 of the superior auricular surface of tibia 12. Baseplate 44 typically has a maximum thickness extending between surfaces 46and 48 in a range between about 1 mm to about 4 mm. Projecting fromsecond 52 of base plate 44 is a stem 54. Stem 54 is configured to beslidably received within socket 42 of guide brace 32. A projection 56downwardly extends from bottom surface 48 of base plate 44 at first end50. As depicted, projection 56 has the configuration of a narrow finger.In other embodiments, projection 56 can comprise an elongated ridge orother configurations.

Formed on second end 40 of guide brace 32 is an enlarged housing 60having a passage 62 extending therethrough. A resiliently flexible clamparm 64 is mounted to housing 60. An aperture 66 extends through clamparm 64 in general alignment with passage 62.

Tubular guide sleeve 36 slidably extends through passage 62 and aperture66. Guide sleeve 36 has a proximal end 68 and an opposing distal end 70.A plurality of sharpened teeth 72 are formed at distal end 70. Bypressing clamp arm 64 toward housing 60, passage 62 and aperture 66 arealigned allowing guide sleeve 36 to freely slide within passage 62 andaperture 66 to a desired location. As clamp arm 56 is released, clamparm 56 resiliently biases away from housing 60 so as to bind guidesleeve 36, thereby securing guide sleeve 36 in the desired location. Inalternative embodiments, it is appreciated that clamp arm 64 can bereplaced with a set screw, clamp, or a variety of other types offasteners that can be used to selectively secure guide sleeve 36 tosecond end 40 of guide brace 32.

During use, as depicted in FIG. 3, template 34 is slid over medial facet24 of tibia 12 so that projection finger 56 catches on posterior side 19of tibia 12. Projection finger 56 thus facilitates proper positioning oftemplate 34 and also, helps to retain template 34 on medial facet 24. Itis appreciated that the size and shape of the lateral and medial facetsof the superior articular surfaces of the tibia varies between differentpatients. As such, the present invention comprises a plurality ofalternative templates 34 which are configured for placement on one ofthe lateral and medial facet and which each have a differentconfiguration. As such a number of the alternative templates 34 can beinitially test fitted to determine one that has a best fit for aparticular patient.

For example, depicted in FIG. 2A is one alternative template 34A that issmaller than template 34. Like elements between templates 34 and 34A areidentified by like reference characters. In further contrast to template34, template 34A has a projection 56A downwardly extending from secondend 52 of base plate 44. Projection 56A thus biases against anteriorside 18 or medial side 16 of tibia 12 to help properly position template34A. In yet other embodiments, in contrast to positioning the projectionon one of the opposing ends of base plate 44, the projection can bepositioned along one of the opposing sides of base plate 44 so as tobias against lateral side 14 (when used on lateral facet 22) or biasagainst medial side 16 of tibia 12.

Once template 34 is selected and properly positioned on medial facet 24,tubular guide sleeve 36 is advanced within housing 60 so that teeth 72at distal end 70 bias against medial side 16 of proximal end 10 of tibia12. Guide sleeve 36 is then secured in place by releasing clamp arm 64.By securing guide sleeve 36 against tibia 12, guide assembly 30 isclamped onto tibia 12. In one alternative embodiment, guide sleeve 36can be biased against anterior side 18 of tibia 12.

Next, a tubular drill sleeve 76 is inserted into tubular guide sleeve60. Positioned within drill sleeve 76 is a guide wire 78. Using drillsleeve 76 as a guide, guide wire 78 is drilled through tibia 12 untilguide wire 78 reaches template 34, thereby forming a guide tunnel. Inpart, template 34 functions as a shield to prevent guide wire 78 and/orother drill tools from accidentally contacting and damaging the femur.In other embodiments, a hole or recess is formed on template 34. Guidewire 78 can passed through or into the hole or recess to ensure completeformation of the tunnel on medial facet 24.

Once the guide tunnel is formed, guide wire 78 and drill sleeve 76 areremoved from guide sleeve 60. A larger drill tool, not show, such as alarger guide wire, drill bit, or the like is then passed through guidesleeve 60 and drilled through tibia 12 along the guide tunnel to form afinal tunnel 90 (FIG. 4) through tibia 12. It is appreciated that anynumber of progressively larger drill tools can be used. In alternativeembodiments guide wire 78 and drill sleeve 76 can be eliminated. Asingle larger drill tool can then be used to form tunnel 90 in a singlepass. Using a sequence of larger drill tools, however, helps ensureproper placement of tunnel 90 and facilitates forming the opening of thetunnel adjacent to template 34.

As discussed below in greater detail, the angular orientation of tunnel90 is typically held constant and is based on the configuration of theimplant. However, depending on the amount of bone needed to be resectedfor mounting the condylar implant, it may be necessary to shift theposition of tunnel 90 posterior or anterior. Shifting the position oftunnel 90 posterior-anterior is accomplished by selectively moving stem54 of template 34 further into or further out of socket 42 of guidebrace 32. Once template 34 and guide brace 32 are positioned at theirrelative positions, a set screw 80 is tightened so as to secure template34 and guide brace 32 together. Predefined markings 82 are formed onstem 54 to help define the relative positioning between template 34 andguide brace 32.

Once tunnel 90 is formed, guide assembly 30 is removed so as to producetibia 12 shown in FIG. 4. As depicted, tunnel 90 has an interior surface92 that extends from a proximal end 94 to an opposing end distal end 96.Proximal end 94 is formed on medial side 16 of proximal end 10 of tibia12. Distal end 96 is formed on medial facet 24 of tibia 12. Althoughtunnel 90 can be any desired size, in one embodiment tunnel 90 has adiameter in a range between about 5 mm to about 10 mm.

Using the above discussed methods and instruments, tunnel 90 is formedby procedures that are minimally invasive to the patient. As discussedbelow in greater detail, once tunnel 90 is formed, tunnel 90 can then beused to assist in the resection of medial fact 24 and/or the mounting ofa condylar implant on the resected medial facet 24. Furthermore, byusing tunnel 90 the resection of medial facet 24 and the mounting of thecondylar implant can also be performed using procedures that areminimally invasive.

Although not required, in one embodiment as mentioned above tunnel 90 isused in the resection of tibia 12 for preparing tibia 12 to receive acondylar implant. The resection of tibia 12 can be accomplished using anumber of different procedures. For example, as depicted in FIG. 5, isone embodiment of a rasp assembly 100 is used in association with aretention rod 102 to facilitate resection of tibia 12.

As depicted in FIG. 6, rasp assembly 100 comprises a rasp body 104having a pivot arm 105 mounted thereon, a rasp guide 106, and a coverplate 108. More specifically, as depicted in FIGS. 6 and 7, rasp body104 has a top surface 110 and an opposing bottom surface 112 that eachextend between a proximal end 114 and an opposing distal end 116.Transversely extending across bottom surface 112 are a plurality ofridges 118 that each terminate at a sharpened cutting edge 120. It isappreciated that ridges 188 and cutting edges 120 can be at any desiredorientation or combination of different orientation that facilitatecutting. Bottom surface 112 is configured such that reciprocatingmovement of bottom surface 112 on tibia 12 produces a recess on tibia 12that can receive a desired implant. Recessed on top surface 110 of raspbody 104 is a guide slot 122. Guide slot 122 is bounded by a floor 124and a sidewall 126 upstanding from floor 124. Extending through floor124 to bottom surface 112 is an opening 128.

Rasp guide 106 comprises a slide plate 130 having a top surface 131 andan opposing bottom surface 133. Downwardly projecting from bottomsurface 133 are a pair of spaced apart forks 132A and 132B with a pin134 extending therebetween. Forks 132A and B have facing interiorsurfaces 136 which bound a gap 137 and have opposing exterior surfaces138. Forks 132A and B terminate at a free terminus 140. Exterior surface138 of each fork 132A and B is recessed at terminus 140 such that asloping shoulder 142 is formed on each fork 132A and B.

Rasp guide 106 is received within guide slot 122 so that forks 132A andB project through opening 128. Rasp guide 106 is slightly smaller thanguide slot 122 such that forks 132A and B are free to reciprocate withinopening 128 as slide plate 130 reciprocates within guide slot 122. Asshown in FIG. 5, cover plate 108 is secured within guide slot 122 so asto retain rasp guide 106 within guide slot 122. Cover plate 108 can bemounted using conventional techniques such as welding, press fit, andthe like. Holes 144 are formed through cover plate 108 to preventunwanted build-up of resected bone particles within guide slot 122.

As depicted in FIG. 6, pivot arm 105 has a proximal end 146 and anopposing distal end 148. A set hole 149 extends through pivot arm 105toward proximal end 146. Distal end 148 of arm 105 is hingedly mountedto proximal end 114 of rasp body 104 by a pin 150.

In one embodiment, an insertion handle 160 is used to place rasp body104 over medial facet 24 of tibia 12. Insertion handle 160 has aproximal end 162 and an opposing distal end 164. A post 165 is formed aproximal end 162. Post 165 is adapted to receive an extension handle ifdesired. A pair of spaced apart lips 166A and B project from distal end164 and bound a slot 163. A channel 168 (FIG. 5) longitudinally extendsthrough insertion handle 160 so as to communicate with slot 163. Channel168 is configured to receive pivot arm 105 when rasp body 104 isreceived within slot 163.

During use, pivot arm 105 is slid into channel 165 from between lips166A and B. Lips 166A and B are then advanced to extend above and belowproximal end 114 of rasp body 104. A set screw 168 (FIG. 7) is thenadvanced into insertion handle 160 so as to extend through set hole 149on pivot arm 105. In this configuration insertion handle 160 rigidlysupports rasp body 104 so as to prevent hinged movement of rasp body 104during insertion.

Turning to FIG. 8, retention rod 102 comprises a tubular set rod 172bounding a channel 174 extending from a proximal end 176 to an opposingdistal end 178. Distal end 178 terminates at a distal end face 179. Ahandle 180 outwardly projects from proximal end 176 to facilitatinggrasping retention rod 102.

Retention rod 102 further comprises a hook rod 182. Hook rod 182 has aproximal end 184 and an opposing distal end 186. Projecting from distalend 186 is a hook 188. Threads 190 are formed on proximal end 184. Aknob 192 is also provided having a threaded port 193. Threads 190 onhook rod 182 are configured to mate with threaded port 193 of knob 192.Hook rod 182 is received within channel 174 of set rod 172 such thatknob 192 biases against handle 180 and hook 188 extends beyond distalend face 179. In this configuration, rotation of knob 192 relative tohook rod 182 causes hook 188 to extend or retract relative to set rod172.

During operation, as depicted in FIG. 5, rasp assembly 100 is mounted onmedial facet 24 of tibia 12. Rasp assembly 100 is positioned using therigidly mounted insertion handle 160, as discussed above, such thatforks 132A and B (FIG. 7) are aligned with the distal end of tunnel 90.Once rasp assembly 100 is positioned, retention rod 102 is advancewithin tunnel 90 from proximal end 94. As depicted in FIG. 9A, knob 192is rotated so that hook 188 extends beyond set rod 172. With hook 188freely exposed, hook 188 is hooked over pin 134 extending between forks132A and B.

As depicted in FIG. 9B, once hook 188 has captured pin 134, knob 192 isrotated so as to advance set rod 172 toward hook 188. Set rod 172 isadvanced until distal end face 179 of set rod 172 biases againstshoulders 142 of forks 132A and B. Shoulders 142 are sloped such thatend face 179 can sit flush against shoulder 142 while set rod 172retains its orientation within tunnel 90. In this configuration,retention rod 102 is securely fixed to rasp guide 106.

Once retention rod 102 is secured to rasp assembly 100, insertion handle160 is removed from pivot arm 105. A reciprocal driver, such as areciprocal saw, not shown, is then connected pivot arm 105. Whileholding rasp guide 106 substantially stationary by holding ontoretention rod 102, the reciprocal driver rapidly reciprocates rasp body104 so that cutting edges 120 resect medial facet 24 of tibia 12. In oneembodiment, rasp body 104 reciprocates along a length in a range betweenabout 1 mm to about 4 mm. Other dimensions can also be used.

In one embodiment bottom surface 112 of rasp body 104 slightly arched.By having pivot arm 105 hingedly attached to rasp body 104, rasp body104 is free to reciprocate along the arched path. The hinged attachmentalso helps to minimize binding of rasp body 104. In alternativeembodiments, arm 105 can be rigidly attached to rasp body 104.

In one embodiment of the present invention means are provided forremovably engaging retention rod 102 with rasp body 104 such that raspbody 104 can be selectively reciprocated without substantial movement ofretention rod 102. By way of example and not by limitation, oneembodiment of the means comprises rasp guide 106 slidably mounted onrasp body 104 and hook 188 mounted on retention rod 102. In alternativeembodiments it is appreciated that a variety of different structures canaccomplish the same function. For example, pin 134 and hook 188 can bereplaced with a threaded connection, bayonet connection, or any numberof other conventional connections which allows retention rod 102 toengage with rasp guide 106.

It is also appreciated that rasp guide 106 can be mounted on rasp body104 in a variety of different ways. For example, opening 128 can extendthrough rasp body 104 without the formation of guide slot 122. In thisembodiment slide plate 130 can be positioned directly on top surface 110of rasp body 104 while forks 132A and B extend through opening 128. Inyet another alternative, guide slot 122 can be formed on bottom surface112 of rasp body 104. Cover plate 108 can be formed having opening 128extending therethrough and cutting edges 120 formed on a bottom surfacethereof. Slide plate 130 can be positioned within the guide slot 122 sothat when cover plate 108 is secured over guide slot 122, forks 132A andB extend through opening 128 formed on cover plate 108.

It is also appreciated that retention rod 102 can have a variety ofdifferent configurations. For example, in alternative embodiments setrod 172 can be eliminated. As such, retention rod 102 can simplycomprise hook rod 182. Furthermore, as discussed above, hook 188 can bereplaced with a variety of different types of connectors.

Once medial facet 24 has been sufficiently resected by rasp body 104,rasp assembly 100 and retention rod 102 are removed. The resected boneparticles are removed by conventional flushing and suction. As depictedin FIG. 10, tibia 12 now has a resected recess 194 formed on medialfacet 24.

It is appreciated that the resection of tibia 12 can be accomplishedusing a variety of different techniques. For example, in one alternativedepicted in FIG. 11, the resection of tibia 12 is accomplished bycutting through an area bounded by a cutting template 200. Cuttingtemplate 200 comprises a plate 202 having a top surface 204 and anopposing bottom surface 206. In the embodiment depicted cutting template200 is configured to rest on lateral facet 22 of tibia 12. Of course,cutting template 200 can also be designed for resting on medial facet24.

Extending between opposing surfaces 204 and 206 are a plurality of guidespaces 208. Guide spaces 208 are formed so that when cutting template200 is positioned, guide spaces 208 are positioned over at least aportion of the facet to be resected. In the embodiment depicted, guidespaces 208 have the configuration of an elongated channel. As will bediscussed below in greater detail, the channels facilitate guidedreceipt of a cutting burr 210 which is used to selectively remove theunwanted bone. In alternative embodiments, depending on the type andsize of tool used to remove the bone, guide spaces 208 can come in avariety of different sizes, shapes, and orientations.

In one embodiment, although not required or shown, a second cuttingtemplate is provided having guide spaces extending therethrough. In thesecond cutting template, the guide spaces are aligned so as to bound thearea of the facet to be resected which was blocked by plate 202 ofcutting template 200. As a result, by sequentially using both cuttingtemplates, all or at least a greater proportion of the bone can beremoved by cutting burr 210. Additional cutting templates can also beused.

Cutting template 200 is used in association with retention rod 102 aspreviously discussed. In the embodiment depicted, handle 180 has adifferent configuration. During use, cutting template 200 is positionover lateral facet 22. Distal end 178 of set rod 172 is advanced throughtunnel 90 so that hook 188 of hook rod 182 projects out of set rod 172.Hook 188 is passed though a guide space 208 and then pulled back ontotop surface 204 of plate 202. A rib 212 upwardly projects from plate 202adjacent to guide space 208. Hook 188 is hooked over rib 212 so as toimprove the engagement between hook 188 and cutting template 200.

Once hook 188 is engaged to cutting template 200, knob 192 is rotated soas to bias set rod 172 against bottom surface 206 of template 200. As aresult, retention rod 102 is securely clamped to cutting template 200.Accordingly, by pulling retention rod 102, cutting template 200 issecurely held in place on lateral facet 22. Cutting burr 210 or someother form of drill bit is then advanced into and along each of guidespaces 208 so as to resect the portion of the bone directly below guidespace 208. As previously discussed, in one embodiment cutting template200 can be removed and replaced with a second template. Burr 100 canthen be passed through guide spaces of the second template to removefurther bone that was covered by cutting template 200.

In other alternatives, it is appreciated that once cutting template 200is removed, the remaining bone portion can be removed by sight and feelwithout the use of a template. In yet other embodiments, depending onthe type and amount of bone needed to be resected, a single template canbe rotated or shifted on lateral facet 22 so that the single template isused to remove the desired bone.

In one embodiment of the present invention, means are provided forremovably engaging retention rod 102 to cutting template 200 so thatretention rod 102 secures cutting template 200 to the lateral or medialfacet of tibia 12 when retention rod 102 is received within tunnel 90 oftibia 12. By way of example and not by limitation, one embodiment ofsuch means comprises hook 188 and guide space 208 which enables hook 188to engage with cutting template 200.

The present invention also envisions that there are a variety of otherstructures that can accomplish the same function. For example, the samestructures and techniques as discussed above for securing retention rod102 to rasp assembly 100 can also be used with cutting template 200.That is, in one alternative forks 132A and B with pin 134 can be mountedon bottom surface 206 of plate 202. Other connections such as threadedconnection, bayonet connections, and the like can also be used.

By using the above discussed instruments and methods, the lateral andmedial facets of tibia 12 can be selectively resected by procedures thatare minimally invasive.

Depicted in FIGS. 12A-12C is one embodiment of a condylar implant 300incorporating features of the present invention. The term “condylarimplant” is broadly intended to include implants that can replace all ora portion of a condyle of a tibia. Accordingly, while the depictedembodiments show one conventional size and configuration for a condylarimplant, in alternative embodiments the condylar implant can be largerto replace more of the tibia or can be smaller to replace only a sectionof a condyle of a tibia. In such alternatives, the condylar implant canhave a variety of different configurations.

Condylar implant 300 comprises a bearing plate 302 having a stem 304projecting therefrom and an inlay 320. More specifically, bearing plate302 comprises a top articular surface 306 and an opposing bottom surface308. In one embodiment, top articular surface 306 is contoured to matewith a corresponding femoral condyle.

A pocket 316 is recess on bottom surface 308. Pocket 316 is bounded by afloor 317 and a sidewall 318 upstanding around the perimeter thereof.Stem 304 projects from bottom surface 308 and terminates at a distalterminus 310. Recessed within distal terminus is a threaded socket 312.Bearing plate 302 and stem 304 are typically comprised of a metal suchas chromium, cobalt, titanium, or the like and alloys thereof but canalso be made of ceramics or plastics. Bearing plate 302 and/or stem 304can also be comprised of layers or sections of different materials. Inone embodiment, bearing plate 302 has a maximum thickness typically in arange between about 2 mm to about 10 mm. Other dimensions can also beused depending on the amount that the tibial condyle is resected or wornaway.

In one embodiment of the present invention, means are provided forconnecting a fastener to stem 304. One example of such means comprisesthreaded socket 312 as discussed above. In alternative embodiments, thethreads within the socket on stem 304 could be replaced with bayonetslots, bayonet posts, ribs which are configured to mate with barbs orother forms of connectors. The socket can also be filled with anadhesive. In still other embodiments, the socket can be eliminated andthreads, bayonet posts, barbs or other forms of connections can beformed on the exterior of stem 304.

Secured within pocket 316 so as to encircle stem 304 is inlay 320. Inlay320 is comprised of a porous bone ingrowth material such as poroustantalum. Other conventional porous bone ingrowth materials can also beused. Inlay 320 is secured within pocket 316 using conventionaltechniques such as press fit, welding, adhesive, and the like. Inlay 322has an exposed bottom surface 322 that can be substantially flat,arched, or can have any other desired configuration.

Centrally extending through stem 304 is a central longitudinal axis 314.In one embodiment, stem 304 projects from floor 317 so as to form anangle θ between central longitudinal axis 314 and inlay 320 in a rangebetween about 30° to about 60°. Other angles can also be used. Stem 304typically has a length in a range between about 2 mm to about 10 mm.Other dimensions can also be used.

It is appreciated that condylar implant 300 can have a variety ofalternative configurations. For example, stem 304 is primarily formed toprovide sufficient room for socket 312 when bearing plate 302 has arelative small thickness. As the thickness of bearing plate 302increases, stem 304 can be increasingly shortened as more of socket 312can be formed directly into bearing plate 302. As such, in someembodiments stem 304 can be eliminated in that all of socket 312 can beformed directly on bearing plate 302.

Furthermore, in the depicted condylar implant 300, pocket 316 is formedto receive inlay 320. In alternative embodiments pocket 316 can beeliminated and a section of the porous bone ingrowth material can bemounted on the bottom surface of bearing plate 302 using otherconventional fastening techniques such as adhesives, screws, alternativepress fits, and the like. Furthermore, in contrast to one pocket 316, ait plurality of spaced apart pockets can be formed on bottom surface 308with each pocket receiving a separate inlay 320. Here it is noted thatspikes, fins, or other forms of projections can also be formedprojecting from bottom surface 308 of bearing plate 302. Theseprojections can penetrate into the tibia or be received within slotsformed on the tibia to help prevent movement of bearing plate 302.

In still other embodiments, it is appreciated that inlay 320 or otherforms of the porous bone ingrowth material can be eliminated. In thisembodiment, the condylar implant can comprise a single integral member.For example, depicted in FIG. 13 is an alternative embodiment of acondylar implant 300A. Implant 300A is formed as a single integralmember having top surface 306 and bottom surface 308. Because of theincreased thickness of implant 300A, stem 304 is eliminated. Threadedsocket 312 is formed directly on bottom surface 308. Projections 309extend from bottom surface 308.

In yet another alternative embodiment, depicted in FIG. 14 is a condylarimplant 326. Like elements between condylar implants 300 and 326 areidentified by like reference characters. In contrast to condylar implant300 which is fixed and rigid, condylar implant 326 is mobile.Specifically, condylar implant 326 comprises a lower bearing plate 328from which stem 304 projects and an upper bearing plate 330 that isslidably mounted on lower bearing plate 328.

As depicted in FIGS. 15A and B, lower bearing plate 328 has a topsurface 332 and an opposing bottom surface 334 with a perimeter edge 335extending therebetween. Pocket 316 is formed on bottom surface 334 toreceive inlay 320. Top surface 332 is substantially flat or inwardlyarched and extends between an anterior end 336 and a posterior end 338.A track 340 is recessed on top surface 332. Track 340 has an open mouthextending through perimeter edge 335 at anterior end 336 andlongitudinally extends toward posterior end 338. Track 340 is bounded bya substantially flat floor 343 having a sidewall 344 upstandingtherefrom. Sidewall 344 comprises a recess groove 345 which extendsalong floor 343 and an outwardly projecting lip 346 which projects alongtop surface 332. As such, the opposing sidewalls 344 of track 340 form amortis.

Upper bearing plate 330 comprises top articular surface 306 and a bottomsurface 348 which each extend between an anterior end 350 and anopposing posterior end 352. Bottom surface 348 has a configurationsubstantially congruent to top surface 332 of lower bearing plate 328.Projecting from bottom surface 348 is an elongated key 354 which extendsfrom toward anterior end 350 to toward posterior end 352. Key 354 has asidewall 356 that is substantially complementary to sidewall 344 of tack340 such that key 354 forms a tenon that can slide into track 340 frommouth 342. In this position key 354 can freely slide along track 340 butis prevented from vertically separating from track 340.

During use, upper bearing plate 330 can slide posterior-anterior onlower bearing plate 328 as the femoral condyle rotates on top articularsurface 306. This ability of upper bearing plate 330 to slide minimizeshigh stress points between the femoral condyle and upper bearing plate,thereby minimizing wear. Furthermore, because bearing plates 328 and 330slide against each other on congruent surfaces, both of bearing plates328 and 330 can be comprised of metal without producing undue wear. Inother embodiments, bearing plates 328 and 330 can be comprised ofplastics, ceramics, or composites of different materials. In addition,bearing plates 328 and 330 can be made of the same or differentmaterials.

Although key 354 and track 340 are shown as being linear, in alternativeembodiments they can be congruently curved to more naturally correspondto the bending movement of the knee. For example, depicted in FIGS. 16Aand B is another alternative embodiment of a condylar implant 360 whichincludes an upper bearing plate 361 and a lower bearing plate 362. Inthis embodiment, lower bearing plate 362 includes a track 363 that iscurved along the length thereof. Upper bearing plate 361 includes anelongated key 364 having a curve complementary to track 363 such thatkey 364 can freely slide within track 363. As previously discussed, key364 and track 363 can also be arched or curved in a vertical plane.

The present invention also provides means for connecting a fastener tothe bottom surface of the bearing plate of a condylar implant. Examplesof such means include stem 304 with threaded socket 312 or the otheralternatives to threaded socket 312 as discussed above. Other examplesof such means comprise the formation of threaded socket 312 directly ona bearing plate as depicted in FIG. 13. In other alternatives, thethreads of socket 312 can be replaced with barbs, bayonet connectors,adhesive, or other alternative forms of connectors.

Depicted in FIG. 17 is one embodiment of an anchor assembly 370 used tosecure condylar implant 300 to tibia 12. Anchor assembly 370 comprises afastener 372, a bone anchor 374, and a crown nut 376. Fastener 372comprises an elongated shaft 380 having an exterior surface 381extending between a proximal end 382 and an opposing distal end 384. Inone embodiment, fastener 372 has a length greater than 8 mm and morecommonly greater 15 mm. Other dimensions can also be used.

Formed at distal end 384 of shaft 380 are threads 386 that areconfigured to threadedly mate with threaded socket 312 of stem 304.Outwardly projecting proximal of threads 386 is an annular flange 388which functions as a stop when fastener 372 is threaded into stem 304.Recessed into proximal end 382 is a socket 390. A pair of opposingbayonet slots 392 longitudinally extend through the sidewall boundingsocket 390. Finally, encircling and radially outwardly projecting fromexterior surface 381 between proximal end 382 and flange 388 areengagement threads 394.

As depicted in FIG. 18, condylar implant 300 is mounted within recess194 such that stem 304 is received within distal end 96 of tunnel 90. Afastener driver 400 has a distal head 402 (FIG. 17) that is configuredto be received within socket 390 of fastener 372. A pair of opposingbayonet prongs 404 project from head 402 and are configured to matewithin bayonet slots 392. With fastener driver 400 secured to proximalend 382 of fastener 372, fastener driver 400 is used to advance distalend 384 into tunnel 90 through proximal end 94. Fastener 372 is advancedthrough tunnel 90 so that threads 386 are received within socket 312 ofstem 304. Fastener driver 400 is then rotated so that fastener 372 isthreaded into stem 304.

Next, bone anchor 374 is secured within tunnel 90. In one embodiment, atap, not shown, is used to initially thread interior surface 92 oftunnel 90. This can be accomplished before or after positioning offastener 372. Alternatively, bone anchor 374 can be self-tapping.

As depicted in FIG. 17, bone anchor 374 comprises a tubular body 410having a substantially cylindrical configuration. Body 410 includes aninterior surface 412 and an exterior surface 414 that each extendbetween a proximal end 416 and an opposing distal end 418. Distal end418 includes a tapered nose 420. Encircling and radially outwardlyprojecting from exterior surface 414 are one or more helical threads422. As mentioned above, the threads can be conventional or self-taping.In alternative embodiments, threads 422 can be replaced by ridges,barbs, or other bone engaging structures used in conventional boneanchors. Bone anchor 374 can be formed of a biocompatible metal, abioabsorbable polymer, a bioactive ceramic, or any other desiredmaterial.

As depicted in FIG. 19, interior surface 412 bounds a channel 424longitudinally extending through bone anchor 374. Interior surface 412comprises a first sidewall 426 extending from proximal end 416, a secondsidewall 430 extending from distal end 418, and an annular shoulder 432extending between first sidewall 426 and second sidewall 430. Firstsidewall 426 has a maximum diameter that is greater than the maximumdiameter of second sidewall 430. As such, shoulder 432 is tapered so asto constrict from first sidewall 426 to second sidewall 430. Firstsidewall 426 bounds a socket 430 which is configured to receive a toolfor rotation of bone anchor 374. As such, first sidewall 426 has anon-circular transverse cross section. In typical embodiments, firstsidewall 426 has a polygonal transverse cross section.

Turning to FIG. 20, a distal end 435 of a tubular anchor driver 436 isreceived within engagement socket 438 of bone anchor 374. Distal end 435has a polygonal configuration complementary to socket 438 such thatrotation of anchor driver 436 rotates bone anchor 364. Bone anchor 374and anchor driver 436 are passed over the proximal end of fastenerdriver 400 and advanced to proximal end 94 of tunnel 90. By rotatinganchor driver 436, bone anchor 374 is screwed into tunnel 90 usingfastener driver 400 as a guide. Bone anchor 374 is sized so that threads422 engage with interior surface 92 of tunnel 90, thereby securing boneanchor 374 to tibia 12 within tunnel 90. Bone anchor 374 is advanced sothat bone anchor 374 encircles engagement threads 394 of fastener 372.Using fastener driver 400 as a guide for bone anchor 374 helps toconcentrically dispose bone anchor 374 around fastener 372.

Once bone anchor 374 is positioned, anchor driver 436 is removed andcrown nut 376 is positioned. As depicted in FIG. 17, crown nut 376comprises a rounded head 440 having a threaded bore 442 extendingtherethrough. Projecting from head 440 are a plurality of spaced apartprongs 444 having notches 446 formed therebetween. Crown nut 376 isconfigured to mate with a nut driver 450. Nut driver 450 comprises atubular shaft 452 that terminates at a distal end 454. Projecting fromdistal end 454 are a plurality of spaced apart prongs 456. Prongs 456are configured to mate with crown nut 376 by being received withinnotches 446. In this mated configuration, rotation of nut driver 450facilitates rotation of crown nut 376.

Turning to FIG. 21, with crown nut 376 mounted on nut driver 450, crownnut 376 and nut driver 450 are passed over the proximal end of fastenerdriver 400. Nut driver 450 is used to advance crown nut along fastenerdriver 400, into tunnel 90, and over fastener 372. Threaded bore 442 ofcrown nut 376 is configured to threadedly mate with engagement threads394 on fastener 372. Accordingly, once crown nut 376 is advanced overfastener 372 to engagement threads 394, nut driver 450 is rotatedcausing crown nut 376 to threadedly engage with engagement threads 394.

As depicted in FIG. 22, socket 428 of bone anchor 374 is larger thanhead 440 of crown nut 376 such that crown nut 376 can freely passtherethrough. Shoulder 432, however, constricts to a diameter smallerthan the diameter of head 440 of crown nut 376. Accordingly, crown nut376 is advanced along fastener 372 by engaging with threads 394 untilhead 440 of crown nut 376 biases against shoulder 432 of bone anchor374. Tightening crown nut 376 against shoulder 432 produces tension onfastener 376 which tightly secures condylar implant 300 against tibia12.

In one embodiment, engagement threads 394 on fastener 372 rotate in adirection opposite threads 422 on bone anchor 374. For example,engagement threads 394 can be right-hand threads while threads 422 areleft-hand threads. As a result, rotation of crown nut 376 against boneanchor 374 does not cause bone anchor 364 to rotate concurrently.Furthermore, once crown nut 376 is initially positioned, nut driver 450is removed. Anchor driver 436 can then be repositioned over fastenerdriver 400 so as to engage with bone anchor 374. Anchor driver 436 canthen be used to back bone anchor 374 a distance back toward proximal end94 of tunnel 90. In so doing, fastener 372 is further tensioned so as toincrease the force securing condylar implant 300 on tibia 12. Again,because threads 394 and threads 422 rotate in opposite directions,backing bone anchor 374 does not cause crown nut 376 to unscrew.

Finally, once crown nut 376 and bone anchor 374 are positioned in theirfinal state, fastener driver 400 is removed from fastener 372. Closingprocedures for the tissue are then performed.

As discussed above, fastener driver 400 is useful as a guide indirecting placement of bone anchor 374 and crown nut 376. In contrast tobeing separately connected to fastener 372, in one alternativeembodiment the fastener driver can be integrally formed with fastener372. For example, depicted in FIG. 23 is a fastener system 460. Fastenersystem 460 includes a fastener 462 and an elongated drive rod 464integrally formed with fastener 462. Like elements between fasteners 372and 462 are identified by like reference characters. As with fastener372, fastener 462 includes flange 388 and threads 386 and 394. Formedproximal of threads 394 is a mating region 468. Mating region has apolygonal or other non-circular transverse cross section. As suchremoval or further tightening of fastener 462 can be accomplished bypassing a tubular driver over fastener 462 so as to engage with matingregion 468.

In contrast to socket 390 of fastener 372, fastener 462 is integrallyformed with drive rod 464. To facilitate separation of drive rod 464from fastener 462, a plurality of annular breaking grooves 466 encirclefastener system 460 at spaced apart locations along the junction betweenfastener 462 and drive rod 464.

Fastener system 460 is used in substantially the same manner as fastener372 and fastener driver 400. However, once bone anchor 374 and crown nut376 are finally positioned, fastener 462 and drive rod 464 are separatedby breaking fastener system 460 at a annular breaking grooves 466located adjacent to proximal end 94 of tunnel 90.

It is appreciated that the anchor assembly for condylar implant 300 canhave a variety of different configurations. For example, depicted inFIG. 24 is an alternative embodiment of an anchor assembly 480. Anchorassembly 480 includes bone anchor 374, as discussed above, and afastener 482. Like elements between fasteners 372 and 482 are identifiedby like reference characters. Fastener 482 includes a shaft 483 having aproximal end 484 and an opposing distal end 486. Mounted at or towarddistal end 486 are threads 386 and flange 388 as discussed above.Mounted at proximal end 484 is an enlarged rounded head 488 thatterminates at an end face 490. Recessed within end face 490 is a sockethaving a polygonal or other non-circular configuration. It is noted thathead 488 has a maximum diameter that is smaller than the diameter ofsocket 424 of bone anchor 374 but larger than the minimum diameter ofshoulder 432 of bone anchor 374. As such, head 488 seats againstshoulder 432 when passed through bone anchor 374.

Turning to FIG. 25, in contrast to anchor assembly 370 where fastener372 is initially positioned, in anchor assembly 480 bone anchor 374 isinitially secured within tunnel 90 using anchor driver 436. Again,tunnel 90 can be pre-tapped or threads 422 on bone anchor 374 can beself-tapping. Once bone anchor 374 is positioned, a driver, not shown,is inserted within socket 492 of fastener 482. The driver is then usedto advance distal end 486 of fastener 482 into tunnel 90, throughchannel 424 of bone anchor 374, and into socket 312 of condylar implant300. The driver is then used to rotate fastener 482 so that threads 386threadedly engage with socket 312. Fastener 482 is advanced into socket312 until flange 388 contacts the end face of stem 304. The driver forfastener 482 is then removed.

Next, anchor driver 436 is inserted back into socket 428 of bone anchor374. This can be accomplished by passing anchor driver 436 over thedriver for fastener 482 or by first removing the driver for fastener482. Anchor driver 436 is then used to back bone anchor 374 a distancetoward proximal end 94 of tunnel 90. In so doing, shoulder 432 of boneanchor 374 biases against head 488 of fastener 482, thereby tensioningfastener 482 so as to securely bias condylar implant 300 against tibia12. It is appreciated that threads 386 of fastener 482 and threads 422of bone anchor 374 rotate in opposite directions so that the backing ofbone anchor 374 does not unscrew fastener 482 from condylar implant 300.

It is appreciated that in alternative embodiments the various threadedconnections used in association with the anchor assemblies can bereplaced with bayonet connections, expanding collets, press fit barbconnections, and other conventional connections commonly used in placeof thread connections.

By using the above discussed condylar implants and anchor assemblieswith the corresponding methods, it is appreciated that the condylarimplants can be securely mounted to tibia 12 using procedures that areminimally invasive.

In other alternative embodiments, it is also appreciated that variouscondylar implants can be designed for implanting in a minimally invasiveprocedure which may or may not require the formation of a tunnel throughtibia 12. For example depicted in FIGS. 26A and B is an alternativeembodiment of a condylar implant 500 incorporating features of thepresent invention. Condylar implant 500 comprises a bearing plate 501having a top articular surface 502 and an opposing bottom surface 504which each extend between an anterior end 506 and a posterior end 508.Although not required, in the embodiment depicted, a pocket 510 isformed on bottom surface 504 to receive an inlay of bone ingrowthmaterial (not shown).

Downwardly extending from bottom surface 504 at anterior end 506 is amounting flange 512. A pair of spaced apart holes 514 and 515 extendthrough mounting flange 512.

During use, medial facet 24 is resected so as to received condylarimplant 500. The resection can be preformed at least in part using theprocedures as discussed above by forming tunnel 90. Alternatively, otherconventional techniques can be used to resect medial facet 24 withoutthe formation of tunnel 90. In either embodiment, a portion of themedial or anterior face of tibia 12 is also resected so as to receivemounting flange 512. Once mounting flange 512 is positioned, screws areadvanced through holes 514 and 515 into the lateral, medial, or anteriorside of tibia 12 so as to directly screw condylar implant 500 to tibia12.

In an alternative embodiment, it is also appreciated that stem 304 ofcondylar implant 300 can be mounted on bottom surface 504 of condylarimplant 500. In this embodiment, condylar implant 500 can be mountedboth through the use of stem 512, as discussed above, and by screwspassing through holes 514 and 515.

Depicted in FIGS. 27A and B is still another alternative embodiment of acondylar implant 530. Condylar implant 530 comprises a bearing plate 532having a top articular surface 534 and an opposing bottom surface 536which each extend between an anterior end 538 and a posterior end 540. Apocket 542 is formed on bottom surface 536. Pocket 542 is bounded by afloor 544 and a sidewall 546 upstanding around the perimeter of floor544. Extending through sidewall 546 at anterior end 538 are a pair ofspaced apart holes 548 and 550.

Centrally projecting from floor 544 is a post 552 having substantiallyt-shaped configuration. In alternative embodiments post 552 can be anydesired configuration. Pocket 542 is designed to partially receive aninlay of bone ingrowth material (not shown) so as to encircle post 552.

During use, a slot complementary to post 552 is formed on the resectedfacet of the tibia. Condylar implant 530 is then positioned on theresected facet so that post 552 is received within the slot. Screws arethen passed through 550 and 552 at a downward angle so as to penetrateinto the tibia. Here it is appreciated that the inlay of bone ingrowthmaterial will also need to have corresponding holes extendingtherethrough so that the screws can pass through the bone ingrowthmaterial into the tibia.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method for mounting a tibial condylar implant, the methodcomprising: forming a tunnel having a proximal end on a lateral, medial,or anterior side of a proximal end of the tibia and a distal end on anat least partially resected lateral or medial facet at the proximal endof the tibia; positioning a condylar implant over the distal end of thetunnel; advancing a fastener into the tunnel from the proximal end ofthe tunnel; and securing the fastener at least partially disposed withinthe tunnel to the condylar implant.
 2. A method as recited in claim 1,wherein the act of forming the tunnel comprises: positioning a templateover the lateral or medial facet of the tibia; biasing a tubular guidesleeve against the lateral, medial, or anterior side of the proximal endof the tibia; and passing a drill tool through the guide sleeve and intothe tibia so as to form the tunnel.
 3. A method as recited in claim 1,wherein the condylar implant comprises a bearing plate and a stemprojecting from a bottom surface of the bearing plate, the act ofpositioning the condylar implant comprising inserting a least a portionof the stem within the distal end of the tunnel.
 4. A method as recitedin claim 1, wherein the act of advancing the fastener into the tunnelcomprises: removably securing a driver to the fastener; and using thedriver to advance the fastener into the tunnel.
 5. A method as recitedin claim 1, wherein the fastener has a drive rod integrally attachedthereto, the method further comprising severing the drive rod from thefastener after the fastener is secured to the condylar implant.
 6. Amethod as recited in claim 1, further comprising advancing a tubularbone anchor into the tunnel from the proximal end of the tunnel so thatthe bone anchor engages with the tibia and encircles at least a portionof the fastener secured to the condylar implant.
 7. A method as recitedin claim 6, wherein the act of advancing the tubular bone anchorcomprises advancing the tubular bone anchor over a driver extending fromthe fastener.
 8. A method as recited in claim 6, securing a crown nut tothe fastener so that the crown nut biases against the bone anchor andthereby tensions the fastener.
 9. A method as recited in claim 8,wherein the act of securing the crown nut to the fastener comprisesscrewing the crown nut onto a portion of the fastener disposed withinthe bone anchor.
 10. A method as recited in claim 8, further comprisingbacking the bone anchor a distance back toward the proximal end of thetunnel so as to further tension the fastener.
 11. A method as recited inclaim 1, further comprising advancing a tubular bone anchor into thetunnel from the proximal end of the tunnel so that the bone anchorengages with the tibia, the fastener being advanced into the tunnelafter placement of the bone anchor such that at least a portion of thefastener passes through the bone anchor.
 12. A method as recited inclaim 11, wherein the act of securing the fastener to the condylarimplant comprises screwing the fastener into the condylar implant sothat the fastener biases against bone anchor.
 13. A method as recited inclaim 11, further comprising rotating the bone anchor so as to advancethe bone anchor toward the proximal end of the tunnel after the fasteneris secured to the condylar implant.
 14. A condylar implant for mountingon the proximal end of a tibia, the condylar implant comprising: abearing plate having a top articular surface and an opposing bottomsurface, the top articular surface being adapted to mate with a femoralcondyle; a stem downwardly projecting from the bottom surface of thebearing plate; and means for connecting a fastener to the stem.
 15. Acondylar implant as recited in claim 14, wherein the stem has a centrallongitudinal axis and the stem is oriented so as to form an anglebetween the central longitudinal axis of the stem and the bottom surfaceof the bearing plate in a range between about 30° to about 80°.
 16. Acondylar implant as recited in claim 14, wherein the bearing platecomprises: a lower bearing plate having the stem projecting therefrom;and an upper bearing plate having the top articular surface formedthereon, one of the lower bearing plate and upper bearing plate having atrack formed thereon while the other has a key that slidably rideswithin the track.
 17. A condylar implant as recited in claim 16, whereinthe key has the configuration of a tenon while the track comprises amortis configured to slidably receive the tenon.
 18. A condylar implantas recited in claim 14, further comprising: the bottom surface of thebearing plate having a pocket formed thereon; and an inlay being securedwithin the pocket.
 19. A condylar implant as recited in claim 18,wherein the inlay comprises a porous bone ingrowth material.
 20. Acondylar implant as recited in claim 19, wherein the pocket and theinlay encircle the stem.
 21. A condylar implant as recited in claim 14,wherein the means for connecting the fastener to the stem comprises athreaded socket formed on the stem.
 22. A condylar implant as recited inclaim 14, wherein the bearing plate and the stem are integrally formedand are each comprised of a medical grade metal.
 23. A condylar implantas recited in claim 14, wherein the bearing plate has a maximumthickness in a range between about 2 mm to about 10 mm.
 24. A condylarimplant as recited in claim 14, wherein the stem has a length in a rangebetween about 2 mm to about 6 mm.
 25. A condylar implant as recited inclaim 14, further comprising a mounting flange downwardly projectingfrom the bottom surface of the bearing plate at a perimeter edge of thebearing plate, the mounting flange bounding at least one hole extendingtherethrough.
 26. A condylar implant system comprising: the condylarimplant as recited in claim 14, and a fastener configured tomechanically engage with the stem.
 27. A condylar implant system asrecited in claim 26, wherein the fastener comprises a shaft havingthreads formed thereon.
 28. A condylar implant system as recited inclaim 27, further comprising an enlarged head integrally formed on theshaft or an enlarged crown nut removably mountable on the shaft.
 29. Acondylar implant system as recited in claim 26, further comprising atubular bone anchor removably encircling at least a portion of thefastener.
 30. A condylar implant system as recited in claim 29, whereinthe fastener has external threads that rotate in a first direction andthe bone anchor has external threads that rotate in a second directionthat is opposite of the first direction.
 31. A condylar implant systemas recited in claim 29, wherein the bone anchor has an interior surfacebounding a channel extending between a first end and an opposing secondend, the first end terminating at a first end face, the channelcomprising a first channel portion extending from the first end, asecond channel portion extending from the second end, and a radiallyinwardly projecting shoulder disposed between the first channel portionand the second channel portion.
 32. A condylar implant for mounting onthe proximal end of a tibia, the condylar implant comprising: a bearingplate having a top articular surface and an opposing bottom surface, thetop articular surface being adapted to mate with a femoral condyle; asection of porous bone ingrowth material mounted on the bottom surfaceof the bearing plate; and means for connecting a fastener to the bottomsurface of the bearing plate.
 33. A condylar implant as recited in claim32, wherein the bearing plate comprises: a lower bearing plate havingthe bottom surface formed thereon; and an upper bearing plate having thetop articular surface formed thereon, one of the lower bearing plate andupper bearing plate having a track formed thereon while the other has akey that slidably rides within the track.
 34. A condylar implant asrecited in claim 33, wherein the key has the configuration of a tenonwhile the track comprises a mortis configured to slidably receive thetenon.
 35. A condylar implant as recited in claim 33, furthercomprising: the bottom surface of the bearing plate having at least onepocket formed thereon; and the section of porous bone ingrowth materialcomprising an inlay being secured within the at least one pocket.
 36. Acondylar implant as recited in claim 33, wherein the means forconnecting a fastener to the bottom surface of the bearing platecomprises a threaded socket from on the bottom surface of the bearingplate.
 37. A condylar implant as recited in claim 33, wherein the meansfor connecting a fastener to the bottom surface of the bearing platecomprises a stem projecting from the bottom surface of the bearingplate, the stem bounding a threaded socket.
 38. A condylar implantsystem for use on the proximal end of a tibia, the system comprising: acondylar implant comprising a bearing plate having a top articularsurface and an opposing bottom surface; an elongated fastenerselectively mountable to the bottom surface of the bearing plate; and atubular bone anchor removably encircling at least a portion of thefastener.
 39. A condylar implant system as recited in claim 38, whereinthe condylar implant further comprises a stem projecting from the bottomsurface of the bearing plate, the stem being configured to mate with thefastener.
 40. A condylar implant system as recited in claim 38, whereinthe fastener mounts to the bearing plate so as to form an inside anglebetween the fastener and the bottom surface of the bearing plate in arange between about 30° to about 80°.
 41. A condylar implant system asrecited in claim 38, wherein the bearing plate comprises: a lowerbearing plate having the bottom surface formed thereon; and an upperbearing plate having the top articular surface formed thereon, one ofthe lower bearing plate and upper bearing plate having a track formedthereon while the other has a key that slidably rides within the track.42. A condylar implant system as recited in claim 38, furthercomprising: the bottom surface of the bearing plate having at least onepocket formed thereon; and an inlay comprised of a porous bone ingrowthmaterial being secured within the at least one pocket.
 43. A condylarimplant system as recited in claim 38, wherein the fastener comprises anelongated shaft having a length in a range between about 5 mm to about15 mm.
 44. A condylar implant system as recited in claim 38, wherein thefastener comprises an elongated shaft having an enlarged head integrallyformed thereon.
 45. A condylar implant system as recited in claim 38,further comprising an enlarged crown nut removably mountable to thefastener.
 46. A condylar implant system as recited in claim 38, whereinthe bone anchor comprises one or more threads or barbs formed on anexterior surface thereof.
 47. A condylar implant system as recited inclaim 38, wherein the fastener has at least one helical thread thatengages with the condylar implant and the bone anchor has at least oneexternal helical thread, the helical thread of the bone anchor rotatingin a direction opposite of the helical thread of the fastener.
 48. Acondylar implant system as recited in claim 38, wherein the bone anchorhas an interior surface bounding a channel extending between a first endand an opposing second end, the first end terminating at a first endface, the channel comprising a first channel portion extending from thefirst end, a second channel portion extending from the second end, and aradially inwardly projecting shoulder disposed between the first channelportion and the second channel portion.
 49. A condylar implant system asrecited in claim 48, wherein the fastener comprises a shaft having anenlarged head integrally formed thereon, the head being biased againstthe shoulder of the bone anchor.
 50. A condylar implant system asrecited in claim 48, further comprising an enlarged crown nut removablymounted on the fastener and biased against the shoulder of the boneanchor.
 51. A condylar implant system as recited in claim 38, furthercomprising a drive rod integrally formed with the fastener, a pluralityof spaced apart annular breaking grooves being formed at theintersection between the fastener and the drive rod.
 52. A condylarimplant for mounting on the proximal end of a tibia, the condylarimplant comprising: a bearing plate having a top articular surface andan opposing bottom surface that each extend to an outer perimeter edge,the top articular surface being adapted to mate with a femoral condyle;and a mounting flange downwardly projecting from the bottom surface atthe perimeter edge, the mounting flange bounding at least one holeextending therethrough.
 53. A condylar implant as recited in claim 52,further comprising: the bottom surface of the bearing plate having apocket formed thereon; and an inlay comprised of a porous bone ingrowthmaterial being secured within the pocket.
 54. A condylar implant formounting on the proximal end of a tibia, the condylar implantcomprising: a bearing plate having a top articular surface and anopposing bottom surface, a recessed pocket being formed on the bottomsurface, the pocket being bounded by a perimeter sidewall, the sidewallbounding at least one hole extending therethrough; and an inlaycomprised of a porous bone ingrowth material being secured within thepocket so that the hole through the sidewall remains openly exposed onboth sides of the sidewall.